This section provides background information related to the present disclosure which is not necessarily prior art.
Critical shortages of water have created great distress for many populations around the world. A great need exists, therefore, particularly throughout the developing world, for safe and reliable supplies of fresh water for human consumption and use. A number of methods, such as desalination of sea water by distillation, currently exist for providing fresh water. Only limited technology is currently available that utilizes the energy from sunlight to accomplish purification via distillation. Further, this limited technology tends to be inefficient, bulky, and difficult to move or install quickly.
For example, a device known as a solar still is a water desalination/purification device that includes an insulated basin that contains a maintained level of brine (or otherwise contaminated water or other fluid amenable to purification by distillation—all hereinafter referred to simply as “brine” for brevity). The brine is of, or maintained at, a concentration within a range compatible with both distillation in the conditions expected, and the need to allow for flow in a given design. To that end, the brine may be introduced by direct filling, or through an inlet, and may be released through an outlet. The basin is typically arranged such that the basin and the brine contained therein are exposed to solar irradiation that warms the brine and causes evaporation. The basin further includes a transparent cover panel (typically of glass) that is inclined. As the brine evaporates, fresh water condenses on the inclined cover panel and drains toward a trough that collects the fresh water and directs it out of the solar still, where it can subsequently be used for drinking or some other use. Such a configuration is relatively simple, compact, and inexpensive. Such a configuration, however, is also very inefficient.
Another solar distillation technology that is often used for seawater desalination and purification is commonly referred to as a Humidification Dehumidification Desalination (HDD) system. The HDD system operates essentially on the same principle as the solar still, but requires the use of two columns or towers. In the HDD system, a circuitous flow of an air/water vapor mixture is induced by spraying (or otherwise introducing) a brine mist into a humidification tower, within which an upward draft of airflow is maintained, and into which some or all of the brine mist is evaporated. The evaporation rate is dependent, in large part, on the temperature of the brine, which is typically raised by an external solar collection device via a heat exchanger. Unevaporated brine falls into a brine reservoir accessible from the base of the humidification tower. The humidified air (air/water vapor mixture) continues to move upward, and is then ducted to the top of a dehumidification tower where it is directed downward. Within this second tower, a series of coils (or other suitable heat exchange medium) into which unheated brine from the aforementioned brine reservoir flows. This unheated brine is at such a temperature that the relatively warm air/water vapor mixture flowing across the coils is cooled sufficiently to induce condensation of fresh water onto the coil surface. The condensation drips off the coils into a collection reservoir at the base of the tower. The heat deposited into the coils via this condensation is then transferred to the initially unheated brine, which therefore exits the coils at an increased temperature. In turn, this “preheated” brine is directed to further heating by the aforementioned external heat exchanger, and is directed as previously described into the humidification tower. The air/water vapor mixture that had passed over the coils and released some or all of its moisture content (i.e., dehumidified air) is now ducted across to the base of the humidification tower, where it is exposed to the incoming spray of brine, and the cycle continues in this manner. The HDD system, however, tends to rather bulky and, therefore, is not very practical in many settings where space is limited or difficult to reach (i.e., in disaster relief settings).
There is a need, therefore, for a solar distillation device that is compact and easily movable, and also high efficiency to obtain maximum yields of fresh water.